Roll Formed Flexible Die Plate For Rotary Cutting Tool

ABSTRACT

A method of making a rotary cutting tool for cutting a web of material comprises the steps of roll forming a first flexible die plate into a cylindrical shape, mounting the cylindrically shaped die plate onto a cylindrically shaped fixture, and machining cutting elements onto the roll formed die plate. The roll formed die plate may then be removed from the fixture and attached to a cylinder. The first die plate can cooperate with a second die plate attached to a second cylinder to cut the thin web of material.

RELATED APPLICATION

This application is a 35 U.S.C. §371 national phase application ofPCT/US2007/060262, filed Jan. 9, 2007, which claims priority benefit ofU.S. provisional patent application No. 60/757,799 filed on Jan. 10,2006.

FIELD OF THE INVENTION

This invention relates to improvements in rotary cutting tools and moreparticularly to improvements in flexible die plates for rotary cuttingtools.

BACKGROUND OF THE INVENTION

Rotary cutting tools are useful for manufacture of carton blanks andother workpieces from sheets or webs of material. In particular, rotarydie cutting tools are used in high speed cutting of a moving sheet orweb of paper, paperboard, plastics or composite materials. As oneexample, rotary die cutting machines are used for the high speed massproduction of paperboard carton blanks that are subsequently folded intothe shape of cartons or boxes such as cereal and cracker boxes, etc.Rotary cutting tools include solid rotary dies, where the cuttingsurface is made part of the cylinders, and flexible rotary dies, where adie plate is wrapped around a cylinder.

It is important that the die plates of flexible dies be properly affixedto the cylinder and aligned, both with respect to the cylinder and withrespect to each other. This is especially important given the speed ofrotation of the die cylinders associated with high volume production.Known techniques for affixing and aligning the die plates includeforming the die plate out of a magnetic material and inserting magnetsinto the die cylinders so that they are magnetically attracted to oneanother. However, such a design greatly increases the costs of the diecylinders for several reasons, including the cost of the magnets, thecost of machining holes into the cylinders to receive the magnets, andthe difficulty in assembly.

In addition, known flexible die plates are formed by a chemical etchingprocess where an acid or base is applied to metal to dissolve awayunwanted material. In practice, a chemical is applied to a flat sheet ofmetal to produce the desired cutting elements on a flexible die plate.The flat flexible die plate is then bent around a cylinder and attachedby one of several methods such as use of strong magnet or welding. Thereare numerous limitations in the chemical etching process, both in termsof limitations in the properties of the die pates made by the processand difficulties in the process for assembling the die plates to thecylinders. For example, tool steels (steels with large amounts ofnon-ferrite alloys) are more difficult to chemically etch. Chemicaletching works better with carbon steels, but carbon steels arerelatively brittle and not ideal for forming, bending and otheroperations. Also, some geometries such as undercuts are difficult tomake. Further, known chemically etched die plates are relatively thin inpart to make them easier to assemble to cylinders. However, thicker dieplates are more desirable as they can be longer lasting and moreresistant to position change.

With regards to the process, use of magnets requires extensive machiningof cylinders, thereby making such cylinders quite expensive. Further,both magnets and welding die plates to the cylinder require extensivechangeover time when switching die plates, undesirably increasingdowntime for printing. Known chemically etched flexible die plates areawkward to assemble with the cylinder. The thin flexible die plates areshipped to the customer as flat plates that are spring-like and resistbending around the cylinder. It would be desirable to provide anenhanced flexible die plate that is long lasting and robust, which iseasy to install with reduced downtime.

SUMMARY OF THE INVENTION

In accordance with a first aspect, a method of making a rotary cuttingtool for cutting a web of material comprises the steps of roll forming afirst flexible die plate into a cylindrical shape, mounting thecylindrically shaped die plate onto a cylindrically shaped fixture, andmachining cutting elements onto the roll formed die plate. The rollformed die plate may then be removed from the fixture and attached to acylinder. The first die plate can cooperate with a second die plateattached to a second cylinder to cut the thin web of material.Optionally the die plate may be roll formed a second time with a radiusgenerally equal to a radius of the cylinder to which the die plate is tobe attached.

From the foregoing disclosure and the following more detaileddescription of various preferred embodiments it will be apparent tothose skilled in the art that the present invention provides asignificant advance in the technology of rotary cutting tools.Particularly significant in this regard is the potential the inventionaffords for providing a high quality, low cost method of making aflexible die plate for a rotary cutting tool. Additional features andadvantages of various preferred embodiments will be better understood inview of the detailed description provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a rotary cutting tool in accordance witha preferred embodiment.

FIGS. 2A-2 c are a series of schematic views of a flexible die plate ofthe rotary cutting tool of FIG. 1, showing the introduction of a radiusto the flexible die plate, and ending in a die plate having a radius.

FIG. 3 is a top side view of the cylinder with the die plate removed,showing the position adjustment devices.

FIG. 4 is an isolated perspective view of a die cylinder adapted toreceive a flexible die plate in accordance with a preferred embodiment.

FIG. 5 is a perspective view of a die cylinder with a flexible die platepulled away to reveal an attachment and alignment device for the dieplates.

FIG. 6 is a close up perspective view of the attachment and alignmentdevice for the die plate.

FIG. 7 is an exploded perspective view of the position adjustmentdevice.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the rotary cutting tool asdisclosed here, including, for example, the specific dimensions of thecutting elements of the flexible die plates, will be determined in partby the particular intended application and use environment. Certainfeatures of the illustrated embodiments have been enlarged or distortedrelative to others to improve visualization and clear understanding. Inparticular, thin features may be thickened, for example, for clarity ofillustration. All references to direction and position, unless otherwiseindicated, refer to the orientation illustrated in the drawings.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

It will be apparent to those skilled in the art, that is, to those whohave knowledge or experience in this area of technology, that many usesand design variations are possible for the rotary cutting tool disclosedhere. The following detailed discussion of various alternative andpreferred features and embodiments will illustrate the generalprinciples of the invention with reference to a rotary cutting toolsuitable for use in industrial applications where flat paperboard-likematerials are to be cut. Other embodiments suitable for otherapplications will be apparent to those skilled in the art given thebenefit of this disclosure.

Referring now to the drawings, FIG. 1 shows a rotary cutting tool 10 inaccordance with a preferred embodiment having an upper die cuttingassembly 96 and a lower die cutting assembly 98. The upper die cuttingassembly has a cylinder 14 and die plate 18 wrapped around the cylinder,and the lower die cutting assembly 98 has a cylinder 16 and a die plate20 wrapped around the cylinder. Each of the assemblies 96, 98 aremounted on a stand 12 so that the cylinders 14, 16 come into closeproximity with one another. The upper cylinder 96 is rotatable aboutaxis 97 and the lower cylinder is rotatable about axis 99, with the axes97 and 99 generally parallel with one another. Each die plate's positionis preferably adjustable with respect to the die cylinder at one or moremounting locations near pins 24, 25.

Each die plate has cutting blades or elements 26, 27, preferably formedas unitary extensions of the corresponding die plate. Cutting elementsare understood here to include broadly any machined changes to the dieplate, including raises, recesses and markings. The cylinders 14, 16 arein registry with one another so that they rotate together. When a thinweb of material (for example, paperboard used to make cereal boxes) isfed between the rotating die plates 18, 20, the cutting elements orblades 26, 27 cooperate to cut the thin web of material into cartonblanks.

In accordance with a highly advantageous feature, the flexible dieplates disclosed herein may advantageously be roll formed prior tomachining cutting elements and prior to installation on thecorresponding cylinder. A curve may be introduced to the flexible dieplate so that the die plate forms a generally cylindrical shape, and aradius of the die plate so produced generally corresponds to the radiusof a cylinder which the die plate is designed to wrap around. FIGS.2A-2C show schematically a flexible die plate gradually rolled into agenerally cylindrical shape which is formed to fit around a cylinder 18.The generally cylindrical shape makes die plates disclosed herein mucheasier to install around a cylinder than known chemically etchedflexible dies. Holes 120 may be formed near corners of the generallyrectangular die plate prior to roll forming, to be used for attachingthe die plate to the fixture and to the die cylinder.

In accordance with a highly advantageous method of manufacture, the dieplates may be roll formed to a cylindrical shape which corresponds tothe cylindrical shape of a fixture. That is, the die plate has about thesame radius as the fixture, and fits snugly on the fixture. Next, thecurved die plate may be mounted on the fixture and machined. In additionto roll forming the flexible die plates, preferably the die plates areheat treated, particularly at the cutting elements. Rockwell hardness ofthe cutting elements of at least 55, and most preferably about 58-60 maybe achieved by heat treating. Moreover, roll-forming the flexible dieplate introduces stress. Application of heat to the cutting elementsrelieves the stress prior to hardening, thereby advantageouslyincreasing the useful life of the die plates.

If the fixture and the cylinder happen to have about the same diameter,the die plate may be removed from the fixture and installed on thecylinder. If not, the machined, generally cylindrical flexible die platemay be roll formed a second time into a generally cylindrical shapeformed to fit around the cylinder used for making carton blanks. Theradius of the flexible die plate so formed is approximately the sameradius as that of the cylinder 18, and most preferably a radius slightlylarger than the radius of the cylinder 18 to allow for snug assembly.Thus, the order of manufacture can comprise first roll forming theunmachined die plate to fit on a fixture cylinder, machining cuttingelements onto the die plate, heat treating the cutting elements,optionally roll forming the die plate a second time to create a dieplate having a radius about the same as a cylinder it will be attachedto, and then assembling the position adjustment devices, magnets and dieplates to the cylinder. After attaching each die plates to itscorresponding cylinder, fine position adjustment can then occur. Infinal assembly, the die plates and cylinders can cut paperboard becausethey are positioned in close proximity to one another as shown inFIG. 1. Because of the speed of installation and the speed ofdisassembly, it is easy to switch products being manufactured. Thus,this method of manufacture of flexible die plates allows for greater useof low volume or limited edition production runs.

FIG. 3 shows a preferred embodiment of a cylinder 14 with the flexibledie plate removed, having a position adjustment device on either side,with each position adjustment device comprising yoke 90 and y-slide 30,discussed in greater detail below. Positioned between the positionadjustment devices are one or more magnets 60. The magnets are used tohelp hold the flexible die plate in place until the fasteners 24, 25 areattached. Bearer surfaces 75 may be provided, extending radially aroundthe axis of rotation a little beyond the cylindrical surface. The bearersurfaces can engage bearer surfaces on an adjacent cylinder and therebyact as protection for the cutting surfaces of the die plates.

FIG. 4 shows the die cylinder 14 of FIG. 3, having a cylindrical surface19 with a constant radius about an axis of rotation 97. Two sides 17extend from either end of the cylindrical surface 19 (only one side isvisible in the perspective view of FIG. 3) generally perpendicular tothe axis of rotation and to the cylindrical surface. A large spacecomprises pocket 62 for the magnets and pockets 64 for the fine positionadjustment devices. When the pockets 62, 64 are combined, they result ina large groove cutaway in the cylindrical surface of the cylinder 14. Afirst opening 39 and a second opening 34 are positioned on each side 17,and connect to the corresponding pocket 64. In certain preferredembodiments the openings 39 and 34 may be formed as a single opening.Openings 79 in pockets 64 of the die cylinder 14 are sized to receivepins for securing the corresponding yokes 90 to the cylinder.

FIG. 5 shows a die plate 18 with the cutting surfaces removed forsimplicity of illustration, leaving only the thick die corners 29 andthe alignment surfaces 111. Alignment surfaces 111 can be used forguidance of the die plate in a second roll forming operation to changethe radius of the die plate to correspond with the radius of thecylinder to which it will be attached as discussed above. The die plateis partially unwrapped around a die cylinder 14, and when installed endsof the die plate meet at the dotted line shown in FIG. 5. Partiallyunwrapping the die reveals a pair of position adjustment devices. Eachposition adjustment device preferably comprises a yoke 90, adjustableslide 30 and various other elements as described in greater detailbelow. The adjustable slides 30 are positioned in yokes 90 which are inturn connected to the die plates remote from the cutting surfaces of thedie plates. More specifically, as shown in the Figs., the adjustableslides 30 are positioned on the underside of the die plate 18, the sideopposite the side of the die plate with the cutting surfaces. In theembodiment shown in the drawings, pair of fixed pins or bolts 73 securethe yoke 90 to the cylinder. Alternatively, one of the fixed pins may bereplaced with an adjustable slide assembly slidable along the X-axis, ifneeded.

FIG. 6 is a close-up view of one of the position adjustment devices.Preferably the die plates are adjustably captivated to the die cylinder.Adjustably captivated as used herein means that the motion of one partwith respect to another part is partially restricted. For example, theadjustable slide 30 is free to slide back and forth with respect to thedie cylinder around the axis of rotation of the die cylinder (along theY-axis labeled in FIG. 6). However, the adjustable slide is captivatedso that it is held in a pocket in the yoke, and cannot leave the pocketalong the Z-axis. In a similar manner the outer eccentric 40 isadjustably captivated to the slide 30, and the inner eccentric 50 isadjustably captivated to the outer eccentric 40.

The pocket in the yoke is preferably oversized, in the sense that theadjustable slide 30 in inserted into the pocket and leaves a gap 55 foradjustment along the Y-axis, and a gap along the X-axis. The topsurfaces of the yoke, slide, first eccentric and second eccentric,respectively, are preferably flush with the outer cylindrical surface ofthe cylinder. That is, these surfaces may be machined down to share acommon radius with the die cylinder 14. An eccentric adjustment screw 38extends through first opening 39 on the side wall to urge the outereccentric 40 to rotate with respect to the adjustable slide. A wedgeadjustment screw 32 extends through second opening 34 and engages awedge 70 to urge the adjustable slide along the Y-axis. First opening 39and second opening 34 may alternatively be formed as a single opening.An adjustable clamp 80 fills up the gap along the x-axis, urging theslide 30 against one wall of the pocket in the yoke.

Yoke 90 has an opening 66 sized to receive pin 24 securing the die plate18 to the yoke. In a similar manner bolt 73 extends through opening 69to secure the yoke to the cylinder. In this manner the flexible dieplate is secured to the cylinder. Other attachment mechanisms may alsobe used.

FIG. 7 is an exploded perspective view of the adjustable slide assembly.Wedge 70 and clamp 80 cooperate to secure the position of the adjustableslide 30. The outer eccentric sits in a cavity in the adjustable slide.The eccentric engagement screw (shown in FIG. 6) engages the outereccentric 40. The outer eccentric engages the adjustable slide.Similarly, the smaller eccentric 50 engages the larger eccentric 40.Opening 67 in the small eccentric 50 receives screw 25, at an opening inthe die plate. The die plate 18 is captivated between the screw 25 andthe slide 30 so that the die plate is adjusted by adjustment of theadjustable slide assembly.

It will be apparent to those skilled in the art, that is, to those whohave knowledge or experience in this area of technology, that many usesand design variations are possible for the flexible die plates disclosedhere. The following detailed discussion of various alternative andpreferred features and embodiments will illustrate the generalprinciples of the invention with reference to a rotary cutting toolsuitable for use in industrial applications where flat paper-likematerials are to be cut. Other embodiments suitable for otherapplications will be apparent to those skilled in the art given thebenefit of this disclosure.

1. A method of making a rotary cutting tool comprising, in combination,the steps of: roll forming a first flexible die plate into a cylindricalshape; mounting the cylindrically shaped die plate onto a cylindricallyshaped fixture; and machining cutting elements onto the roll formed dieplate.
 2. The method of making a rotary cutting tool further comprisingthe step of attaching the die plate to a corresponding cylinder.
 3. Themethod of claim 1 wherein the fixture has a cylindrical, curved surfaceand the curve of the die plate generally corresponds to the curvedsurface of the fixture.
 4. The method of claim 1 further comprising thestep of: removing the die plate from the fixture and roll forming thedie plate a second time, forming the die plate into a generallycylindrical shape.
 5. The method of claim 4 further comprising acylinder having a radius, wherein the generally cylindrical shape of theflexible die plate is has a radius which is about the same size as theradius of the cylinder.
 6. The method of claim 4 further comprising acylinder having a radius, wherein the generally cylindrical shape of theflexible die plate is has a radius which is slightly larger than theradius of the cylinder.
 7. The method of claim 1 further comprising thestep of heat treating the cutting elements formed on the flexible dieplate.
 8. The method of claim 1 further comprising the step ofassembling the flexible die plate and a position adjustment device to acylinder, wherein the position adjustment device provides for positionadjustment of the flexible die plate on the cylinder.
 9. The method ofclaim 8 wherein the position adjustment device comprises a yoke whichreceives a y-slide and at least one eccentric.
 10. The method of claim 8further comprising the steps of: roll forming a second flexible dieplate into a cylindrical shape; mounting the second die plate onto thecylindrically shaped fixture; machining cutting elements onto the rollformed die plate; assembling the second die plate and a second positionadjustment device to a second cylinder; and positioning cylinders withattached die plates in close proximity to one another, allowing the dieplates to cooperate to cut a thin web of material.